CN113543958A

CN113543958A - Method and system for producing gradient polarizing film

Info

Publication number: CN113543958A
Application number: CN201980081927.3A
Authority: CN
Inventors: Z·托卡尔斯基; E·贝格; S·巴拉苏布拉马尼安; H-W·邱
Original assignee: Essilor International Compagnie Generale dOptique SA
Current assignee: EssilorLuxottica SA
Priority date: 2018-12-21
Filing date: 2019-12-09
Publication date: 2021-10-22
Anticipated expiration: 2039-12-09
Also published as: CN113543958B; US20220055327A1; EP3670146B1; EP3670146A1; EP3670146A8; WO2020126622A8; WO2020126622A1

Abstract

A system and method for manufacturing an ophthalmic lens is provided. The method includes preparing a cross-polarization removing optical film for an optical article comprising: providing a film having at least a first section comprising a first edge, a second section comprising a second edge, and a predetermined color intensity; providing an apparatus, wherein the apparatus comprises at least a first roller and a second roller, wherein the first roller and the second roller are configured to stretch at least a portion of the film; and continuously and asymmetrically stretching at least a portion of the film using the apparatus while substantially maintaining the color intensity of the film.

Description

Method and system for producing gradient polarizing film

Technical Field

The present disclosure generally relates to methods and systems for making films for optical articles. More particularly, the present disclosure relates to methods and systems for stretching optical films, stretched optical films produced therefrom, and optical articles incorporating such optical films.

Background

Gradient polarizing films may be used in optical articles such as ophthalmic lenses, polarized sunglasses, and other types of lenses. Polarized sunglasses for outdoor use allow the vertical polarization component of light to be transmitted, which is preferable for clear vision, while eliminating the horizontal polarization component of light. Vertically aligned light is preferred because it coincides with the natural tendency of the human eye to focus on the vertical component of the image. In particular, when the human eye uses a gradient polarizing film outdoors to view devices such as smartphones, GPS devices, tablets, air pump user interfaces, vehicle or aircraft dashboard displays, and other devices with polarized displays, the use of a gradient polarizing film for polarizing lenses can be challenging for the wearer due to the "cross-polarization" effect. This occurs when the image appears black due to the cross-polarization between the polarization of the polarized display and the polarization of the sunglasses. During cross-polarization, the polarization direction of the sunglasses is perpendicular to the polarization direction used by the image being viewed by the viewer.

To address this problem, there is a need for an improved optical film that can be used in optical articles, such as ophthalmic lenses, more specifically polarizing lenses. The optical articles described herein may be ophthalmic lenses or plano lenses that may be used for health and/or solar filter applications. A novel method is provided herein for making improved gradient polarizing films for such ophthalmic lenses using a variable or differential stretching process for making optical films. Such lenses may be prepared by casting, injection molding or additive manufacturing, and may optionally be further tinted using a separate subsequent tinting process.

The differential stretching process described herein for producing optical films includes continuously and asymmetrically stretching a dyed film comprising, for example, poly (vinyl alcohol) (PVA), poly (ethylene terephthalate), or other polarizing matrix material, in a roll-to-roll web-fed stretching process, wherein the film moves from one conversion process to another in a continuous roll-to-roll or die-to-roll machine. Conversion is a change in the structure or composition of the film, such as coating, lamination, stretching, and the like. In this way, a gradient polarizing film can be produced with a first portion of the film stretched to provide maximum polarization and a second portion of the film minimally stretched such that there is little or no polarization in the second portion of the film.

The method of making a gradient polarizing film disclosed herein includes changing the geometry of the pulling rolls used in the roll stretching system from a substantially cylindrical shape to a substantially conical or frustoconical shape to stretch such film. The resulting stretched film has a target stretch ratio and increased Polarization Efficiency (PE) from one edge of the film to the opposite edge, while maintaining the color intensity of the entire optical film during the manufacturing process. Thus, a polarizing film having a gradually and continuously varying Polarization Efficiency (PE) from one edge of the film to the other edge is provided. It should be noted, however, that the color intensity of the film will vary with thickness according to beer's law as described herein.

Other objects, features and advantages of the present invention will become apparent from the following detailed description. However, it should be understood that the detailed description and specific examples, while indicating specific embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

Disclosure of Invention

A method of manufacture is provided herein. The method includes preparing a cross-polarization removing optical film for an optical article comprising: providing a film having at least a first section comprising a first edge, a second section comprising a second edge, a predetermined color intensity, and a thickness; providing an apparatus, wherein the apparatus comprises at least a first roller and a second roller, wherein the first roller and the second roller are configured to stretch at least a portion of the film; and continuously and asymmetrically stretching at least a portion of the film using the apparatus while substantially maintaining the color intensity of the film. The method further includes providing an apparatus wherein the first roller is a substantially cylindrical roller and the second roller is a substantially frustoconical roller. The method further includes stretching the film such that the thickness of the film is reduced from a first thickness to a second thickness, wherein the second thickness is less than the first thickness.

The method further includes stretching at least a portion of the film such that at least a portion of a first segment of the film has a first stretch ratio and a first polarization efficiency and at least a portion of a second segment of the film has a second stretch ratio and a second polarization efficiency. The method further includes stretching the film such that the first stretch ratio and the first polarization efficiency are greater than the second stretch ratio and the second polarization efficiency.

The method further includes stretching the film such that a total stretch ratio of the film, including the first stretch ratio and the second stretch ratio, and a total polarization efficiency, including the first polarization efficiency and the second polarization efficiency, decrease continuously from a first edge of the film to a second edge of the film. The method further comprises providing an apparatus wherein the first roller is a substantially cylindrical roller or a substantially frustoconical roller and the second roller is a substantially cylindrical roller or a substantially frustoconical roller. The method further includes stretching at least a portion of the first section of the film such that it has a stretch ratio of between 1 and 4 and a polarization efficiency of between 90% and 100%.

The method further includes stretching at least a portion of the second section of the optical film such that it has a stretch ratio of less than 3.5. The method further comprises providing a pre-stretched film during the step of providing the film. The method further includes providing a film having a color gradient during the step of providing the film, wherein the color gradient varies continuously from a first edge of a first section of the film to a second edge of the second section. The method further includes further processing the film using at least one of casting, injection molding, additive manufacturing, and tinting.

Also presented herein is an optical article comprising a cross-polarization removing optical polarizing film, wherein the film comprises at least: a first segment comprising a first edge, a first stretch ratio, and a first polarization efficiency; a second segment comprising a second edge, a second stretch ratio, and a second polarization efficiency, wherein the first stretch ratio and the first polarization efficiency are greater than the second stretch ratio and the second polarization efficiency; and a polarization gradient that decreases continuously from a first edge of the film to a second edge of the film, wherein the film is stretched continuously and asymmetrically. The first and second polarization efficiencies comprise a total polarization efficiency, and wherein the total polarization efficiency decreases continuously from the first edge of the film to the second edge of the film. The film has a transmission between 8% and 85%.

Drawings

The advantages, nature, and various additional features as described herein will appear more fully upon consideration of the illustrative embodiments now to be described in detail in connection with the accompanying drawings. In the drawings, like numerals refer to like parts throughout the several views.

FIG. 1 illustrates a system for processing and stretching an optical film.

Fig. 2A shows a side view of a prior art apparatus for stretching an optical film in a "pure stretch mode".

Fig. 2B illustrates a side view of a section of the prior art apparatus of fig. 2A.

Fig. 3A illustrates a front view of a substantially conical or frusto-conical roller used in the system of fig. 3B.

Fig. 3B illustrates a top view of an exemplary roller system that may be used to stretch the film in a "pure stretch mode".

Fig. 3C illustrates a side view of the roller system of fig. 3B.

Fig. 4A illustrates a top view of an exemplary roller system having at least one cylindrical roller and at least one conical roller that can be used to stretch an optical film in a "gap stretch mode".

Fig. 4B illustrates a side view of the roller system of fig. 4A.

FIG. 5 is illustrated in a) Industrial Machine Direction Orientation (MDO); or a side view of a roller system that can be used in b) gradient MDO for a gap stretch mode process for stretching optical films.

Fig. 6A illustrates a pre-stretched optical film that may be used in the stretching process described herein as a "batch process" method.

Fig. 6B shows the portion of the pre-stretched film of fig. 6A stretched over a stationary substantially conical or frusto-conical roller.

Fig. 6C shows the film of fig. 6B after at least a portion of the film has been stretched using a substantially conical or frustoconical roller and removed from the roller.

Fig. 7A illustrates an exemplary roller system that may be used to stretch an optical film in a "continuous stretch mode".

Fig. 7B shows the film of fig. 7A before being stretched by conical rolls on the left side and after being stretched by conical rolls on the right side in the continuous stretch mode of fig. 7A.

Fig. 8 shows a top view of the film winding device.

Detailed Description

The words or terms used herein have their ordinary, plain, meaning in the art of this disclosure, except to the extent explicitly and clearly defined in this disclosure or unless a specific context requires otherwise a different meaning.

If there is any conflict in the use of a word or term in this disclosure and in one or more patents or other documents that may be incorporated by reference, a definition that is consistent with this specification shall be adopted.

The indefinite article "a" or "an" refers to one or more than one of the element, part or step introduced by the article.

Whenever a numerical range with a lower and upper limit on the degree or measurement is disclosed, it is also intended to specifically disclose any number and any range falling within the range. For example, each range of values (in the form of "from a to b," or "from about a to about b," or "from about a to b," "from about a to b," and any similar expressions where "a" and "b" represent numerical values of degree or measurement) should be understood to clarify each number and range that is encompassed within the broader range of values and includes the values "a" and "b" themselves.

Terms such as "first," "second," "third," and the like may be arbitrarily assigned and are merely intended to distinguish two or more components, parts, or steps that are similar or corresponding in nature, structure, function, or effect. For example, the words "first" and "second" are not used for other purposes and are not part of the name or description of the name or descriptive terms that follow. The mere use of the term "first" does not require the presence of any "second" like or corresponding parts, features or steps. Similarly, the mere use of the word "second" does not require the presence of any "first" or "third" similar or corresponding components, parts or steps. Further, it should be understood that the mere use of the term "first" does not require that an element or step be the very first of any order, but merely that it be at least one of such elements or steps. Similarly, the mere use of the terms "first" and "second" does not necessarily require any order. Thus, the mere use of such terms does not exclude intermediate elements or steps between the "first" and "second" elements or steps, etc.

"continuous" material refers to a length of material that is relatively long, stable, continuous, unbroken, or uninterrupted having one or more properties. A "continuous" (or "continuously") process refers to a process without breaks, gaps, anomalies, or reversals.

"conical" refers to a shape of a cone having an outer surface.

"cylindrical" means having straight parallel sides and a circular or elliptical cross-section; the shape or form of a cylinder having an outer surface.

"film" is generally used to include any material in the form of sheets, nets, tapes, films, foils, rods, filaments and threads.

"frustoconical" refers to a cone with the tip removed, for example having the shape of a cone with a narrow end, or the shape of a cone with the tip removed or truncated. A cone having a region with its apex cut off by a plane is called a truncated cone.

Herein, "gradient" is used to refer to the change in any optical characteristic (such as polarization efficiency or transmittance) from one portion of an ophthalmic lens to another. The gradient described herein is typically gradual, smooth, and continuous. However, such gradients may also be discrete and/or incremental, whether smooth or not.

Herein, the term "lens" is used to refer to an organic or inorganic glass lens, preferably an organic lens, comprising a lens substrate having one or more surfaces, which may be coated with one or more coatings having different properties. As used herein, "lens blank" refers to a transparent medium (without power) having a known base curve, which is used by optical laboratories to produce finished ophthalmic lenses having a prescription power; it is used for single, bifocal and trifocal lenses, and Progressive Addition Lenses (PAL). In non-limiting aspects, the methods of the present invention can be used to prepare transparent and non-transparent (e.g., opaque) articles and devices.

The phrase "organic solvent" refers to any hydrocarbon-based liquid used in the current embodiments having suitable surface tension, density, and/or immiscibility characteristics in water. Exemplary organic solvents include aliphatic and aromatic hydrocarbons (e.g., ethers, petroleum ether, pentane, hexane, hexanes, heptane, heptanes, octane, benzene, toluene, xylene, or the like, or mixtures thereof, or alcoholic solvents, or the like).

Described herein are methods and systems for making optical films of optical articles constructed according to the principles of the present disclosure. The optical articles and methods used herein may be used with any type of ophthalmic lens. In particular embodiments, the optical articles produced herein may be used in lenses for sunglasses or for sun protection purposes. Such lenses may be piano or may have corrective power. The ophthalmic lens may be a polarizing lens. The ophthalmic article may be formed from a plastic optical substrate, which is a lens substrate or a lens blank. The substrate may be a hydrophobic substrate or a hydrophilic substrate. Without being limited by theory, the present invention also includes optical devices and methods of manufacturing optical devices. The optical device may include any device capable of generating, manipulating, or measuring electromagnetic radiation, such as a camera, a visor, binoculars, a microscope, a telescope, a laser, and the like. In certain examples, the optical device may comprise an optical article, such as an ophthalmic article or lens.

"stretch" means making an object longer or wider without tearing or breaking it.

Referring to FIG. 1, a system 46 for processing optical films is shown. The system comprises a plurality of rollers 12 for conveying the film 3 and a plurality of grooves 14 positioned one after the other in the form of assembly lines. In this illustration, the rollers are generally shown as having the same shape or design, but other shapes or designs are contemplated, such as those described herein. Further, the rollers may have different cylinder radius dimensions. Each tank 14 contains various wet solutions for immersing the optical film 3. At least one roller 12 is positioned within a portion of each slot 14. The rollers 12 may be positioned in various configurations relative to each other and the film 3 to be processed.

System 46 is used to process films, necessarily PVA films, containing at least one dichroic dye. Other processing methods may be used to process, stretch and optionally treat the PVA film before it can be used in an optical article, such as an ophthalmic lens, more particularly a sunglass lens. Structures and materials for making light polarizing films from polyvinyl alcohol (PVA) and dichroic dyes may also include those disclosed in U.S. patent nos. 4,859,039, 4,992,218, 5,051,309, 5,071,906, 5,326,507, 5,582,916, and 6,113,811. The disclosures of these patents disclose materials, processes and structures for producing polarizing elements and layers, which are incorporated herein in their entirety. In this case, a transparent PVA film 3(Kuraray Poval PVA film, available from Kuraray gmbh) was used. The film had a thickness of about 75 microns. However, other membranes are contemplated within the scope of the present invention.

The processing steps for preparing the PVA polarizing film are as follows, and as shown in steps 1 to 8: (1) a transparent PVA film 3, in particular a PVA film comprising at least a plasticizer material, is provided. The PVA film may optionally be dried and then soaked in water. The membrane 3 may be soaked in a first tank and subsequently in a second tank. This process involves (2) swelling the clear PVA film 3 in a water bath to remove the plasticizer. The membrane 3 expands about 30% in all dimensions. The process includes further spraying or soaking at least a portion of the film with a "wet solution" as the film 3 travels through each set of rollers 12. Each tank includes a bath having at least one spray head positioned at the outlet of each bath to contain any carryover (e.g., contaminants, pigments) exiting from each tank. During this process, the PVA film absorbs water, softening the film to be stretchable at room temperature. In some cases, variations in the degree of expansion and stretching may occur if the PVA film is not uniformly and sequentially expanded. In this case, a small uniform force may optionally be applied to the membrane 3 to help ensure uniform elongation and uniformity and avoid wrinkles forming in the membrane.

Then, the process further includes (3) soaking the PVA film in a water bath to remove impurities. More specifically, the PVA film was soaked in water at 25 ℃ for 5 minutes until the film contained about 70% -85% water in order to make it soft and elastic. However, the soaking time may depend on the span length in the tank and the membrane speed. In some embodiments, the water-soluble plasticizer may optionally be removed during this step, or the additive may optionally be pre-adsorbed. This process results in a transparent polarizing PVA film 3 which is flexible due to its high water saturation and makes it easier to incorporate additional components (dyes, cross-linking agents, etc.) into the film and to feed the film through the system 46 for further processing.

The process further includes (4) soaking the PVA film in a heated dichroic dye bath in a tank containing a dichroic solution. The center roller, positioned within a portion of the trough containing the dichroic solution, is raised or lowered to control the path length traveled by the film in the trough and, thus, affect the time the film spends in the trough. The dyeing step is carried out by adsorbing or depositing the dye onto the polymer chains of the oriented polyvinyl alcohol film. In other embodiments, this step may be performed before, simultaneously with, or after the stretching step. Depending on the distance between the rollers in the tank or the span length and the overall speed of the assembly line, the film is dyed for 4 minutes at a temperature between about 30 ℃ and about 60 ℃, preferably between about 40 ℃ and about 50 ℃, most preferably at 45 ℃.

After the dyeing step, the process further includes (5) rinsing the PVA film with a water rinse bath at 25 ℃ for 2 minutes to rinse excess dye in the rinse tank. Dye bath 5 is heated to keep the dye in solution. Then, the process further includes (6) immersing and soaking the PVA film in a bath of boric acid crosslinking agent while stretching the film in the crosslinking agent bath/main stretching bath. The boric acid crosslinking tank 6 is heated. Heating the dye solution and boric acid solution helps to reduce or prevent precipitation of the solutions. In another embodiment, the method may further comprise filtering the dye and/or boric acid solution to reduce or prevent precipitation and recrystallization of the dye and boric acid in the tank. Heating of the film helps to reduce the crystallinity of the PVA polymer film host matrix so the film can stretch more and accept more dye guest molecules in the free volume regions between the host polymer molecule backbones. The PVA crystalline domains reform upon cooling and drying.

The concentration of the boric acid crosslinker solution in water is between about 1% and about 5%, more specifically about 2%. In particular, the maximum solubility of the boric acid crosslinker solution at room temperature is 5%. The membrane is soaked in the boric acid solution at a temperature between about 20 ℃ and about 40 ℃, more preferably at a temperature of about 30 ℃, for 1-5 minutes, preferably for about 2 minutes. The boron soaking step is performed to improve resistance to heat, water and organic solvents, improve thermal stability by forming cross-bridges between PVA chains, and form a chelating compound with dye molecules to stabilize the film. In this example, the film was stretched during the boric acid soaking process. In other embodiments, this step may be performed before, simultaneously with, or after stretching the PVA film. Although boric acid is used, other metal compounds including transition metals, such as borax, glyoxal, and glutaraldehyde, may be used. Metal salts (such as acetates, nitrates and sulfates) of the fourth phase transition metals (such as chromium, manganese, cobalt, nickel, copper and zinc) may be used. Metal solutions including any of the following may be used: manganese (II) acetate tetrahydrate, manganese (III) acetate dihydrate, manganese (II) nitrate hexahydrate, manganese (II) sulfate pentahydrate, cobalt (II) acetate tetrahydrate, cobalt (II) nitrate hexahydrate, cobalt (II) sulfate heptahydrate, nickel (II) acetate tetrahydrate, nickel (II) nitrate hexahydrate, nickel (II) sulfate hexahydrate, zinc (II) acetate, zinc (II) sulfate, chromium (III) nitrate nonahydrate, copper (II) acetate monohydrate, copper (II) nitrate trihydrate, and copper (II) sulfate pentahydrate. Any one of these metals may be used alone, and alternatively, a plurality of types of such compounds may be used in combination.

During the process of using the roller system shown in fig. 1, the tension of the rollers stretches the wet film 3. The speed of the rollers 12 gradually increases between the grooves as the film advances from the upstream side 72 to the downstream side 85 of the assembly (see table 1 below). The "upstream roller" roller is described herein as the roller closer to the start of the system line 46, i.e. starting from the roller used in process steps 2 to 4, while the downstream roller is the roller used in steps 5 to 7. For example, to accommodate the extra length of PVA film due to expansion of all dimensions of the film, the roller speed in slot 3 is faster than the roller speed in slot 2. The downstream roll has a higher speed than the upstream roll.

TABLE 1

In this mode, the membrane is placed in the top portion of the tank 14 (FIG. 1) containing the wet solution. The top portion of the trough is the portion closest to the air above the trough, while the bottom portion is the portion closest to the bottom surface of the trough. The stretching of the film 3 is carried out at the bottom part of the tank 14, i.e. the distance or span length between two rolls immersed at the bottom of the tank 14. The maximum amount of stretching of the film 3 occurs in the crosslinking (boric acid) bath 6, followed by stretching of the film 3 in the dye bath 4. Thus, the method further includes incrementally increasing the speed or tangential speed of at least one set of driven rolls of the system 46 to accommodate the stretched film 3. More specifically, the method further includes incrementally increasing the speed of the at least one downstream roll such that it has a faster speed or tangential velocity than the at least one upstream roll. The tangential velocity of the conical rolls or roll speed described herein is a function of the diameter of such rolls. The tangential velocity (m/min) is calculated using the roll diameter x rpm. The cylindrical rolls in motion have only one speed, while the conical or frusto-conical rolls in motion increase in speed as the roll diameter of the conical rolls increases, as will be described in more detail below.

The process then involves (7) rinsing the membrane 3 in a water bath at 25 ℃ for 2 minutes to rinse away excess boric acid. The step of drying the film 3 is then carried out (8) in a convection dryer or drying oven 16. The PVA film is dried at a temperature of about 70 ℃ or greater, preferably at a temperature of between about 90 ℃ to about 120 ℃ for 1 to 120 minutes, preferably 3 to 40 minutes, and most preferably at a temperature of about 80 ℃ for 15 minutes, while maintaining the film in a stretched state. To prevent excessive heating, the moisture evaporated from the PVA film is immediately removed to accelerate the evaporation. The heat resistance of the PVA film depends on its moisture content. This method allows drying of the PVA film while suppressing temperature increase.

After the film is dried, the film may optionally then be passed through a lamination process using a lamination film 26 with TAC (PC, acrylic, COC or other) film. The binder 20 may optionally be added to or combined with the PVA film 3 and subsequently further cured in a curing oven 24. Further, an additional at least one protective liner 33 (if not already present on the TAC film) may optionally be added to at least a portion of the film to produce a final optical film product 18, which may then be used in an optical article, such as an ophthalmic lens. The film may then be wound onto a roll, such as the roll shown in fig. 8. Optionally, the process may include dye dipping the film to add a gradient tint, color, or photochromic agent, or optionally further stretching the film. In one aspect, the film 3 may be protected by lamination between two transparent protective films. To achieve this, an adhesive layer may be used to laminate a transparent protective film or sheet onto the surface of the polarizing film 3. The transparent protective layer that may be used is selected from transparent resins such as triacetyl cellulose (TAC), Cellulose Acetate Butyrate (CAB), polycarbonate, thermoplastic polyurethane, polyvinyl chloride, polyamide, and polymethyl methacrylate.

Stretching step- "pure stretching mode"

The invention disclosed herein focuses on step (6): and (3) stretching the PVA film. With reference to fig. 2A and 2B, conventional film stretching processes, referred to in the art as "pure stretch mode", are described in US 2012/0327512 and US 2547736, both of which are incorporated herein by reference. "pure draw" may be achieved when the "span length" (distance between two draw rolls) is large enough to produce strain hardening, but may not be achieved in all draw processes. In the continuous stretching process, the PVA film is stretched a little while the film travels between the grooves, and then dried in an oven. The maximum stretching of the film occurs during the "D-stretch process" section, as shown in fig. 2B, where three pairs of cylindrical nip rollers (for 2-stage stretching) are shown (although two pairs of cylindrical nip rollers may also be used). In the "pure stretch mode", the film is longitudinally and continuously stretched in its longitudinal direction by a pair of spaced apart pairs of driven nip rollers 48, thereby having opposite tensions. In this method, the cylindrical roller is used only during the film stretching. One of the pulling forces of one of the set of nip rollers 48 is typically of a greater magnitude than the other pair of nip rollers to continuously pull and move the film in the machine direction as the film undergoes stretching and/or deformation.

The film is continuously and longitudinally stretched by pulling it through two spaced sets of rotating rollers 48, each set comprising at least two rotatably mounted nip or nip rollers pressed together between which the film is sandwiched. The opposite pulling force required for stretching is set by rotating the rollers at a greater peripheral speed at the output or downstream end of the apparatus than at the input or upstream end. Thus, a sheet of film may be subjected to stretching between a set of input rolls and a set of output rolls. Due to the pressure contact between the rollers in each set, each freely rotatable roller will rotate at substantially the same peripheral speed as the driven roller in that set. In one embodiment, a Polyethylene (PET) carrier may be used to stretch the PVA film down to 20 microns (for thin electronic display applications). However, for films used in ophthalmic lenses such as polarizing lenses, a carrier is not necessary. Although not shown, the means for driving the input and output rollers 48 may include a servo motor or other prime mover drivingly connected to the power input shaft of the gearbox. The power take-off shaft on the gearbox may be drivably connected to the input roller by a drive chain and suitable sprockets. The power take-off shaft of the gearbox may be arranged to rotate with a suitable speed differential to provide the required speed ratio for the input and output rollers.

Pure drawing using frusto-conical rolls

Referring to fig. 3A-3C, in contrast to the "pure draw mode" known in the art, in applicants' pure draw system, at least a portion of the cylindrical roller 12 in the assembly-line groove 14 is replaced with a substantially conical or frustoconical nip

roller

90, 900 during the drawing step 6, as shown in fig. 3A. The radius of the conical or frusto-conical rollers increases continuously and gradually from a first radius nearest the apex 49 to a second radius furthest from the apex 49, where the second radius is greater than the first radius. In particular, each conical roll has a gradually increasing radius from about 150mm to about 500mm, or approximately, the draw ratio is the ratio of the conical roll radii (R)_{Big (a)}/R_Small). The "base radius" of a circular cone is the radius of its base 58 or the radius of the cone. The terms "substantially conical" and "frustoconical" are used interchangeably herein. Each conical roll 90 has an apex 49 and an apex angle such that the conical radius of the conical roll allows for the production of optical films having a desired gradient of film draw ratio ("SR") (defined below) from a minimum at one film edge to a maximum at the other film edge, as described herein.

The system illustrated in fig. 3B and 3C is used during step 6 of the stretching process shown in fig. 1. As described above, this roller system 170 is positioned within a portion of the trough 14 and includes at least a pair of

cylindrical rollers

100, 1000 and at least two substantially conical/

frustoconical rollers

90, 900. More specifically, the pure stretching process herein for stretching PVA film comprises a system comprising at least two cylindrical rolls on the left or upstream side 72 of the system and at least two substantially conical or frustoconical rolls on the downstream side 85 of the system, as shown in fig. 3B and 3C.

In one aspect, more than one optical film 3 may be stretched at a time. Alternatively, a single film having a large width may be cut or slit in the machine direction into several small segments or lanes, and each segment or lane may be stretched independently. As shown in fig. 3B, a single optical film may be placed in each of lanes a-E such that each film is stretched to have a different stretch ratio. One or more optical films 3 may be fed into a system 170 comprising one or more rollers, each having a radius r 1. In one embodiment, each film 3 or film 3 cut into multiple lanes is placed in film lanes a-E, respectively. The lanes labeled A through E and the increasing diameter cylindrical roll sections are illustrative aids only, such as SR from 1-2 in 0.25 increments. The web, rolls and SR are continuous in practice. As described next to the

cylindrical rollers

100, 1000, each film 3 is stretched so that it has a certain numerical stretch ratio in the range of 1 to 2. On the other hand, a single optical film 3 may be stretched on the lanes a to E. The higher the draw ratio, the longer the sheet of film, as shown.

As shown in fig. 3A and 3B, the first and second supply or

input rollers

100, 1000, on which the unstretched optical film 3 is placed, may be substantially cylindrical. The diameter of each cylindrical roller is from about 150mm to about 450mm for small machines and up to about 900mm for large machines. In particular, typical mulch widths are about 150mm for small laboratory scale units and up to about 1-2 meters for large commercial machines. Most commercial extruded films are about 0.5m to over 2m wide. A wider unstretched film may be cut or sliced into rolls of smaller diameter. Each

roller

100, 1000 has a circumferential outer surface configured to allow the film 3 to rotate along the circumferential inner surface of the

roller

100, 1000 in the direction of the roller 100 (indicated by the arrow).

As shown in fig. 3B and 3C, after being stretched through

cylindrical rollers

100, 1000, optical film(s) 3 are then provided to at least two substantially conical or

frustoconical rollers

90, 900. This configuration can be considered a hybrid type stretcher, combining a pure stretch mode and a gap stretch mode. The film 3 is wound on the roller 90 in a first direction and then wound on the conical roller 900 in a second direction opposite to the first direction. In this embodiment, the average distance between

rolls

100, 1000 and 90, 900 may be between 1-2 meters.

In fig. 3B, the film 3 enters the roll assembly from an upstream process. Typically, one or more films (usually only one film) may enter the nip roll as shown in FIG. 3C. The conical rolls 90, 900 rotate at a higher rpm than the conical rolls and pull and stretch the film 3. Fig. 3B shows a single film 3, the width of which extends from lane a to E. The

rollers

100, 1000 serve to hold the film and prevent the film from slipping when pulled by the

rollers

90, 900. As a visual aid, a trace of the film 3 is drawn in the figure, showing the different pull lengths (draw ratios) due to the different diameter sections of the press rolls 90, 900. Larger diameter roller sections will pull (stretch) the film more than smaller diameter sections.

In another aspect, a wide single film 3 may enter the nip

rollers

100, 1000 where the film is cut into several smaller widths. The slitting knife for slitting the film can be located before or as part of the roll assembly. In this embodiment, every other lane (e.g., A, C, E) is stretched by a separate

conical roller

90, 900 assembly. The conical rolls consist of smaller roll sections, the width of which is only the same as the film track cut. As before, each lane is stretched in proportion to the diameter of the smaller roll.

The draw ratio of the film 3 continuously changes with the conical diameter of the roll. If film 3 comprises iodine, a dichroic dye, or another alignable dye, a gradient polarizing film can be produced with a polarization efficiency that increases from the smaller radius to the larger radius of the conical roll. In pure draw mode, the ratio of the width of each film as it enters each slot to the width of the film as it exits each slot is equal to the ratio of the thickness of the film entering each slot to the thickness of the film exiting each slot. For optical film applications, pure stretching is more preferred than other stretching.

The rollers described herein may be made of or made of resins such as silicone, polyurethane, epoxy, ABS, fluorocarbon, or polymethylpentene resins. The roller may also be obtained by plating with resin. Alternatively, the roller may be made of a material obtained by mixing various metal powders with a resin. Alternatively, the rollers described herein may be constructed of metals such as aluminum, brass, or steel. The metal roller is preferable because it exhibits excellent heat resistance and mechanical strength, is suitable for continuous production and precision molding, is less scratched, exhibits high durability against heat generated by polymerization, and is less deformed.

In equal volume, "pure stretching process" (volume constant stretching): length (L) × width (W) × thickness (T) ═ λ L · W)/(λ of the film^0.5)·T/(λ^0.5) Where λ is the draw ratio (SR). If the optical film 3 is not stretched at all, the stretching ratio is 1. During stretching, the PVA film is continuously and asymmetrically stretched using at least one conical or

frustoconical roller

90, 900, each having a radius that gradually increases in the range from r1 to r2, while being immersed in a boric acid bath to produce a polarizing film. As the film 3 is stretched, the color intensity of the film is maintained, while the thickness of the film is reduced by 1/(λ:)^0.5) Thereby making the film appear lighter in color (beer's law). It should be noted that, according to beer's law (absorbance λ)_max＝log(I₀/I)＝ε_λmaxc · l), the color intensity of the film varies with thickness.

In an exemplary embodiment, PVA film 3 may be stretched to about 4 times its original length and width, and its thickness reduced to about 50% of its original thickness, i.e., about 38 microns.

In one aspect, film 3 may be stretched to have a stretch ratio of between 1 and 4, preferably between 2 and 3.8, preferably less than 3.5, more preferably about 3.3, while having a Polarization Efficiency (PE) of between about 90% and 100%.

The polarization efficiency is related to the degree of alignment of the absorptive component of the dye molecule (dichroic dye or iodine) with the main chain of the PVA molecule in the stretching direction, and is measured in parallel (T;)_║) And perpendicular (T)_┴) The spectral transmittance in the film stretching direction was determined and the formula PE ═ T ═ was used_┴-T_║)/(T_║+T_┴))^0.5To calculate. In another embodiment, the polarizing film may have a stretch ratio of 2 and a polarizing efficiency of between about 40% and about 50%. It should be noted that the human eye cannot perceive a polarization efficiency of less than 50%.

The degree of stretching of the film across the width (W) of the film is proportional to the tension difference created by the conical rolls 90, 900 as a result of the tangential velocity difference across the length (diameter) of the conical rolls. The film 3 is preferably stretched in a substantially flat or substantially planar position and moved under the stretching force applied by the moving rollers such that its longitudinal axis (also indicated by "L" in fig. 3B) is substantially at right angles to the

input rollers

100, 1000 and

output rollers

90, 900. Stretching of the film may also occur by the processes described herein even if the film 3 is not maintained in a substantially flat or substantially planar state in the form of a substantially sheet-like material and even if it may fold, wrinkle or crease.

In one embodiment, a PVA film containing a non-dichroic dye may be stretched to a stretch ratio of 3, but the non-dichroic dye will not align with the PVA molecules in the PVA film, so the polarization efficiency will be 0 in this case, and thus the film will not be polarized.

Mixing roller system

In yet another embodiment, the film 3 may be stretched using a hybrid roller system, wherein the stretching rollers may be partially cylindrical and partially conical or frustoconical in shape. This will allow the film 3 to stretch uniformly over the cylindrical portion of the roll and asymmetrically over the conical or frusto-conical section of the roll. For example, 50% of the roll is conical and 50% is cylindrical, the film rolled up on the outer surface of the cylindrical part of the roll will have any stretch ratio between SR-1 (unstretched) to SR-1'. SR-1 ' may be from SR-1 (unstretched) up to SR-3 or 4, and the stretching ratio using the conical roll section will be SR-1 ' to SR-2 '. For example, if SR 1' ═ SR 1, half of the film is unstretched. If SR 2 ═ SR 3, PE is 99%. This enables the production of an ophthalmic lens without PE in the lower half or lower portion of the ophthalmic lens, and the upper half or top portion of the lens increases from 0% PE in the middle to 99% PE at the top of the lens.

For a constant radius r_cy1Cylindrical roll (standard condition) at an angular velocity of

And the tangential velocity is constant:

for radius from r₁Increase to r₂(e.g. r)₂＝3·r₁) Conical rolls of from 2 pi r in circumference₁Increase to 2 pi · r₂(e.g., substitution)

I.e. three times circumference) and its tangential velocity from

Is continuously increased to

(e.g., substitution)

I.e., three times the tangential velocity).

The stretching ratio (λ ═ x) of the film 3_{Finally, the product is processed}/x_Initial) Continuously as the diameter of the conical rolls and if film 3 contains iodine, dichroic dyes or other alignable dyes, the polarization efficiency of the gradient polarizing film increases from the smaller radius to the larger radius of the conical rolls. Because the top portion is thin, using a larger radius may allow reflection from film wedges that may be formed by a thickness gradient, thereby directing light upward.

After the film 3 is stretched, the length of the stretched film 3 varies over its entire width, and therefore the stretched film 3 must be conveyed and wound by conical or frustoconical rollers after being stretched in order to prevent the film from being shaken in the weft direction and forming a loosely wound film roll. Alternatively, the film may be wound in a film winding device (fig. 8) as described below.

Pure stretching mode-gradient stretching

In another exemplary embodiment, a "pure stretch" mode may be used to stretch the PVA film, particularly using gradient stretching. This process involves soaking, swelling, dyeing and cross-linking the PVA film as described in the steps above. The roller system (not shown) for stretching PVA film 3 consists of a first pair of nip rollers 100, 1000 (which are substantially cylindrical on the left or "upstream" side of the roller system), a second pair of nip rollers 90, 900 (which are substantially conical on the right of the first pair of nip rollers), and (if further film stretching is to be performed on the right of the second pair of nip rollers) a third pair of substantially conical rollers (not shown). In this embodiment, all downstream rollers are substantially conical, including the roller located in the furnace, after the first pair of substantially cylindrical rollers. Prior to stretching, the film 3 will be a first length. After stretching, the film will have a second length that is half the length of the first length. For example, the width of the PVA film used may be about 1 meter prior to stretching. After the PVA film 3 was stretched, its width was half a meter, and the stretching ratio was > 3.3. In pure stretch mode, the ratio of film width to film thickness remains constant during and after stretching of the film. For constant W/T pure stretch, the draw ratio of gap stretch increases because the film width is limited.

Gap stretch mode

Referring to fig. 4A and 4B, another embodiment of a roller system for stretching a PVA film is shown. This embodiment is referred to as "gap stretch mode". In this embodiment, the first and second

cylindrical rollers

13, 61 function as feed rollers for receiving the film 3. The first cylindrical roller has a first diameter and the second cylindrical roller 61 has a second diameter greater than the first roller 13. The rollers may be of any size. However, smaller rollers are better due to space constraints in typical assemblies. The roller 13 prevents the film on the roller 61 from slipping in the downstream direction when the roller 15 pulls and stretches the film. In one aspect, a similar roller is positioned on roller 15 to prevent the film from slipping in the upstream direction. The first and

second rollers

13, 61 are positioned close to each other to allow the optical film 3 to simultaneously and continuously contact both rollers during the film stretching process. As PVA film 3 is stretched, the molecules of PVA film 3 become more uniformly aligned and substantially polarized.

Stretching of the polymer in the PVA film also allows alignment of the dichroic dye in the optical film. A PVA film comprising at least one dichroic dye will not have a polarizing effect if it remains unstretched. To produce an ophthalmic lens polarized in one zone (i.e., the top or upper portion closer to the wearer's forehead when worn by the wearer) but not in a second zone (i.e., the lower portion facing away from the wearer's forehead when worn by the wearer relative to the wearer's face), the stretch ratios of the two zones of the optical film used in the lens must be different.

In this gap stretch mode embodiment, an MDO (machine direction orientation) multi-stage machine with short gap stretch conditions may be used to stretch the film in a narrow gap (i.e., a few millimeters to a few centimeters) between the substantially cylindrical roll 61 and the substantially conical or frustoconical roll 15. This narrow gap is important because it affects the strain rate. High strain rates will lead to film cracking because the polymer chains cannot be oriented fast enough. By short gap draw conditions is meant conditions that include dried semi-crystalline films that are heated by the stack of rollers that make up the MDO unit. The tangential velocity of the stretched film 3 roll on the outer surface of the conical roll increases with the diameter of the roll. The increase in tangential velocity increases the stretch ratio of the film proportionally and if the film contains a dichroic dye, a gradient polarizing film will be formed. Polarizing films can be produced using the pure stretch stretching process described herein, under long gap stretch conditions, and using water-plasticized PVA films stretched while submerged in an ionomer solution. Long gap draw conditions include a one meter (several meters) length gap.

When the film 3 passes through the cylindrical roller in the direction indicated by the arrow, the film 3 may be stretched such that the stretch ratio thereof is greater than 1. Then, the film 3 passes under the roller 13 so that it is wound on the outer surface of the roller 13, after which it is wound on the outer surface of the roller 61 in the direction of the arrow, and is maintained at a stretch ratio of 1 while it is wound on the outer surface of the roller 13 in the opposite direction. The film passes through the stretching gap 73 and is then sent to the lower side of the conical roll 15 so that it is wound on the outer surface of the conical roll 15. The drawing gap is a gap between the cylindrical roll 61 and the conical roll 15. A first portion 35 of the film is stretched by a first portion of the conical roll having a diameter greater than the diameter of the remainder of the conical roll. Due to the shape of the tapered rollers, the optical film is stretched 1 to 3 times the original length of the film. As shown, the first portion 35 of the film is stretched to have a stretch ratio of between 2 and 3, while the second portion 47 of the film is held at a stretch ratio of 1. In the gap-draw process, the optical film may be 50% of the final stretched film before being sent to the stretching apparatus. If a final stretch ratio of 4 is desired, the initial stretch ratio of the first section will be 2 before entering the stretch stage using the gap stretch mode.

Gradient drawing

In another embodiment, the film 3 may be stretched to have a gradient stretch. In this embodiment, the optical film has a first section 35 corresponding to the upper portion of the film and a first edge 21. The optical film also has a second section 47 of film corresponding to the lower portion of the film as described above, and a second edge 65. Starting from a constant hue across the width of the film, the gradient stretch process produces a film that is thinner and lighter in color at the edges of the film, and is stretched to a greater degree than at the opposite edges. Thus, the polarization efficiency of the film increases toward lighter shades. Starting from an asymmetrically colored film, the gradient stretch process of the present invention can produce a film that is stretched thinner along the more deeply colored side of the film using a continuous film coloring process similar to that described in US 2015/0261011. The color intensity of the thinner, darker shade will match the intensity of the thicker, lighter shade to produce a constant colored film. The gradient polarization efficiency increases with increasing degree of stretching, i.e., the thinner side of the film.

In yet another embodiment, a polarizing film may be prepared having a stretch ratio of 2 on one edge of the film and a stretch ratio of 3 on the other opposite edge of the film. Films having these characteristics can be made by using the asymmetric film stretching apparatus and process described herein, starting with an unstretched film (stretch ratio of 1), and then stretching one edge of the film up to a stretch ratio of 2 and the other edge up to a stretch ratio of 3. Alternatively, this type of film may be produced using a standard film stretching machine that includes a cylindrical roller and uniformly stretches the film to a stretch ratio of 2. This film with a uniform stretch ratio of 2 can then be continuously and asymmetrically stretched using the apparatus and process described herein to stretch only one edge of the film up to a stretch ratio of 3. In this example, the opposite edges of the film were not stretched additionally and the stretch ratio of 2 was maintained pre-stretched.

Gap stretch mode-MDO

Referring to fig. 5, a roller system 45 is shown in which a PVA film (or other polarisable film) may be stretched in a) gap stretch mode: standard industry MDO or b) gap stretch mode: a gradient MDO. If the rollers used in the process are substantially conical, a gradient will be created. In gap draw mode, standard industry MDO process, PVA film is uniformly stretched as it exits the roller system. In gap draw mode, gradient MDO, the unstretched PVA film is asymmetrically drawn as it exits a cylindrical roller system (nearest roller 44) that uses conical or frustoconical rollers for drawing the PVA film. The rollers are positioned in a substantially horizontal plane. During the gap stretch mode process, the width of PVA film 3 remains constant as the PVA film changes from a first thickness to a second thickness, wherein the second thickness is less than the first thickness. In gap draw mode, the distance between the rolls in a roll system is much shorter than in systems used in pure draw mode. The PVA film produced by the gap stretching method has a different aspect ratio compared to the pure stretching method. In the gap stretch mode, the width to thickness ratio is not constant or increasing, regardless of whether substantially conical or substantially cylindrical rollers are used in the roller system to stretch the PVA film, and regardless of whether motor stretching is used.

In gap draw mode: in standard MDO, the film 3 is wound on 10 large substantially cylindrical rolls (reference numerals 32 to 44). In this system, a five-roll system (pair (F, G, H) on the top 53 of the machine and pair I, J on the bottom 54 of the machine) is used to prevent the film 3 from slipping during stretching. Stretching occurs in the gap 71 between the

rollers

37 and 38. This embodiment includes four temperature zones: zone 1 (rolls 32, 34, 36) preheat, zone 2: stage 1 stretching (rollers 37, 38), zone 3: stage 2 stretching (40, 41): and stage 4: post-draw annealing rolls (42, 43, 44).

Gap stretching mode: gradient MDO

During gap stretch mode-gradient MDO, film 3 is sequentially wound onto the first four cylindrical larger rolls (32, 34, 36, 37) and cylindrical nip rolls F and G. In this embodiment, the

larger rollers

38, 40, 41, 42, 43, 44 are conical or frustoconical, as are the nip rollers H, I and J. The smaller diameter conical rollers are positioned on the operator side of the apparatus 45, while the larger diameter conical rollers are positioned on the motor side. The operator side refers to the front of the machine that is accessible to the operator, while the rear side of the machine is the location where mechanical and electrical components are housed. In fig. 5, the motor is located at the top of the cabinet. In this embodiment, all of the downstream rollers (i.e., 38-44) are substantially conical or frustoconical. In contrast to the standard MDO design described above, the configuration of the machine 45 may not be in the horizontal plane. The method may further include winding the film 3 on the roll 100 in a first direction and then winding the film on the roll 1000 in a second direction opposite to the first direction.

Batch process

Referring to fig. 6A-6C, another embodiment for stretching an optical film, referred to as a "batch process," is illustrated. In this embodiment, the method further includes pre-stretching the unstretched optical film 3 having SR ═ 1 (fig. 6A), which is then stretched by the rollers 15 of the stretching system using one or more conical or frustoconical rollers 15 (fig. 6B), while the sheet is pulled over the rollers 15 and simultaneously thermoformed around a stationary conical mold roller.

In yet another embodiment (not shown), the film 3 may be stretched along a pivot point at its center by a conical roll that is substantially at the center of the film. The pivot point may extend along the length of the centre of the membrane 3. The stretching of the film 3 is greater as it is stretched by the wider section of the conical roll than the narrower portion of the conical roll. Thus, when roller 15 is viewed from its narrower end, in some cases, a film stretched closer to the viewer will be stretched less or not stretched at all than a section of the film that is farther from the viewer.

Fig. 6B is a static device similar to an angled cylinder that is in contact with a static horizontal membrane clamped on both sides. The angled cylinder is raised through the film and contacts one side of the film first, and the film is stretched as each section of the film contacts the cylinder. Alternatively, the central cylinder may have a pivot joint on one side of the membrane while the second side is raised to produce a gradient stretch (the second side has a higher SR).

In another embodiment, the device shown in fig. 6B may be positioned similar to the Intron tensile tester, except that the clamps used to secure the membrane 3 are positioned at an angle relative to each other. The angle between the clamps is used to set the stretch gradient (via the initial film length) from the first side to the second side of the film. In one aspect, clips may be positioned on both sides of the membrane to secure the membrane. In this embodiment, one side of the film would have an unstretched length of 1X, while the other side may have a stretched length of 3X (i.e., if the clips are positioned at a large angle relative to each other). If the extension is stopped after the jig is additionally moved by 2X so that the film is additionally extended by 2X, the length of the short side of the film should be 3X and the length of the other side should be 5X. Thus, the "shorter" side of the film will have a stretch ratio of 3/1 (SR ═ 3), and the longer side of the film will have an SR of 5/3 (SR ═ 1.67).

In these angled cylinder and angled Instron clamp embodiments, the film may be stretched, but the stretching may not be uniform across the length and width of the film. In these embodiments, the film would have to be stretched one at a time. The radius of the roller 15 ranges from a first radius r1 to a second radius r 2. Each of the first portion 35 of the film 3 and the second portion of the film 47 has a stretch ratio of 1 before the film 3 is stretched by the conical roll 15. During stretching of the film 3 by the conical rollers 15, the first portion 35 of the film is stretched such that it has a stretch ratio of between 2 and 3, and the second portion 47 of the film has a stretch ratio of 1 (fig. 6C). As the optical film is stretched, the amount of molecular alignment increases, and the stretch ratio increases from the first edge 65 of the film to the second edge 21 of the film 3. The first portion 35 of the polarizing film 3 may have a final stretch ratio of up to 4, more specifically between 3 and 4, and a polarizing efficiency of up to about 99%. The second section 47 of the optical film 3 has a lower stretch ratio, e.g., less than 3, and a polarization efficiency between about 0% and about 50%.

As shown in fig. 6C, prior to being stretched, the film may have a 1 stretch ratio on the "upstream" side 72 of the film, a stretch ratio between 1 and 3 in the middle section 23 of the film, and a 1 stretch ratio on the downstream side 85 of the film 3 (where a 1 stretch ratio is maintained).

Alternatively, as described herein, a single film sheet may be formed on a substantially conical (or dome-shaped) surface using a batch process to produce a gradient stretched film, wherein the stretched film has a 3-4 times greater stretch from the larger diameter to the smaller diameter of the cone.

Continuous process

Referring to fig. 7A and 7B, an exemplary roller system 17 is illustrated that may be used in a continuous stretching process. The roller system comprises an apparatus having a frame 5 to which various rollers 10 are fixed. As described above, the frame may be immersed in a bath such as a boric acid bath. Current methods of stretching PVA films for optical purposes only involve the use of cylindrical rollers. In the embodiment shown in FIG. 7A, the system includes nine cylindrical rollers. Each cylindrical roller may have a plurality of independent cylindrical segments such that a segment of one end of the cylindrical roller will rotate faster than a segment of the opposite end of the same roller to accommodate different film tangential speeds of the film. Various roller configurations will occur to those of ordinary skill in the art, including the addition of a nip roller system to prevent film slippage and tension isolation. In this embodiment, all of the rollers are substantially conical to convey the film through this portion of the rollers. Although not shown, this embodiment must also include at least one nip roller, which may be used to pull the film similar to an MDO unit (mid-gap stretching device). In this embodiment, the film is continuously stretched, but may not have a final uniform gradient stretch.

In this embodiment, the film 3 may be pulled through a series or plurality of conical rollers 10, allowing the conical geometry to stretch and shape the film 3. In this embodiment, the shape of all the rollers is substantially conical or frustoconical (from the film unwinding unit to the rewinding unit), since the stretched side of the film 3 travels a longer distance than the unstretched side. In this embodiment, a set of nip rollers (not shown) is required to prevent film slippage and tension isolation prior to receipt by the rewind unit. After the film 3 has been stretched by the plurality of rollers 10, rewinding of the film may be performed using a conical core at a lower tension than that used during stretching.

In this "continuous" process, the film 3 is stretched at a slower rate on the upstream side 72 than on the downstream side 85. The PVA film was continuously fed at about 1m/min to a feed roll on the upstream side 72. The membrane exits continuously from the downstream side 85 at about 3 m/min. After the PVA film is stretched, it may have a 3 stretch ratio in the first portion 35 of the film and a 1 stretch ratio in the second portion of the film 47, as shown in fig. 7B.

In this embodiment, the diameter of the conical roll at its widest point is the diameter of the cylindrical roll (d)_cyl.) Three times that of the original. When each conical roller completes the first rotation, the rotation distance of the conical roller is pi.3 d_cyl(1 rotation). Thus, after the film is stretched, the stretched edge 21 at end 67 of the film is eventually longer than the unstretched edge 21 at end 55 of the film, while the unstretched edge 65 at ends 55, 67 remains the same length. After stretching, the difference in length between edge 21 and edge 65 requires a conical re-roll core or pancake re-roll unit (fig. 8). The first portion 35 of the film is stretched more than the second portion 47 of the film 3.

As shown in fig. 7B, the optical film 3 may be stretched such that after the entire film 3 is stretched over the conical rolls 10, there is a stretch ratio of between 2 and 3 in the first portion 35 of the film and 1 in the second portion 47 of the film (fig. 7B). During and after stretching of optical film 3, the polarization efficiency increases from second edge 65 of second portion 47 of film 3 to first edge 21 of first portion 35. During stretching, the same color intensity was maintained throughout the film, thereby producing a gradient polarizing film. Color intensity can be measured by a spectrometer (i.e., Hunter or similar commercially available device). After the film is stretched and placed into an ophthalmic lens, the lens may optionally be tinted. In one aspect, the product may be colored with a gradient tint. Neither "batch" nor "continuous" processes produce uniform stretching across the width of the film. These methods also do not allow tension control across the width of the film or the ability to apply high tension to the film without the use of additional conical rolls.

Other embodiments

In another embodiment, an optical film 3 may be produced having a stretch ratio of 2 at the second edge 65 of the second portion 47 of the film and a stretch ratio of 3 at the first edge 21 of the first portion 35 of the film. This type of film may be produced by using the asymmetric film stretching apparatus and methods described herein. To start the process, an unstretched film with a stretch ratio of 1 was used. The second edge 65 of the second portion 47 is stretched up to a stretch ratio of 2 and the first edge 21 of the first portion 35 is stretched up to a stretch ratio of 3.

Alternatively, to produce the same film described above, a standard film stretching apparatus comprising only cylindrical rollers may be used to uniformly stretch the film to a 2 stretch ratio. Accordingly, the method includes providing an optical film having a stretch ratio of 2, wherein the optical film includes a first portion 35 having a first edge 21 and a second portion 47 having a second edge 65. Next, the asymmetric systems and methods described herein can be used to uniformly stretch only the first edge 21 of the provided film up to a stretch ratio of 3. Thus, first edge 21 has a 3 stretch ratio, while second edge 65 has no additional stretch and remains at a 2 stretch ratio.

Film winding device

Referring to fig. 8, after the film 3 is continuously and asymmetrically stretched, the length of the stretched film varies across its width, and therefore the stretched film must be conveyed and wound by substantially conical or frustoconical rollers in order to prevent the film from sloshing in the weft direction and forming a loosely wound film roll. In addition to winding or collecting the gradient stretched film on a tapered roller, a film winding device may be used to wind or collect the asymmetric film 3 having one side longer than the other side. The film winding device ("wafer winder") comprises a central cylinder 25 having a central axis. The central cylinder 25 is fixed to the base 56. The film winding device further comprises a conical lay-up roller 39 having a first end 75 for holding the minimum stretched portion 47 of the film and the other end 86 for holding the maximum stretched portion 35 of the film, in contact with the already collected film 3 that has been wound on the base 56. The conical roller 39 may rotate in a clockwise direction as shown. As shown, the base 56 may rotate in a clockwise direction. The film winding device allows the stretched film 3 to be wound flat around the central axis, since the shorter, unstretched edge of the film will be wound closer to the central axis than the longer, stretched edge (which will be wound further from this axis).

Ophthalmic lenses produced using the continuous asymmetric methods described herein can have legal driving qualities, for example, having a transmission (% T) between 8% and 85%, more specifically between 8% and 18%. Transmittance describes the total intensity of light passing through the lens, typically expressed as a percentage compared to the initial amount of light incident on the lens. Lenses with high transmission absorb only a low level of light, allowing a high proportion of the light intensity to be transmitted through the lens, which makes them not very useful for sunglass lenses. A lens with very low transmission will absorb very much light, darkening the lens so that it is almost impossible to see through. The polarization efficiency of the lenses produced by the continuous asymmetric process described herein will be higher (i.e. having a stretch ratio of up to 3 or 4) in the stretched portion of the film (up to 99%) and lower (where the stretch ratio is 1) in the unstretched portion of the lens (about 0%). Finally, the lens itself may additionally be tinted to have a uniform% T (with a gradient polarization efficiency). In addition to the invention disclosed herein being useful for improving optical articles such as ophthalmic lenses, the invention disclosed herein may be used in many applications outside the optical industry, for example, electro-optic applications for other types of coatings.

The particular examples disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. It is therefore evident that the particular illustrative examples disclosed above may be altered or modified and all such variations are considered within the scope of the invention. Various elements or steps in accordance with the disclosed elements or steps can be beneficially combined or implemented together in different combinations or sub-combinations of sequences of elements or steps to increase the efficiency and benefits that can be obtained from the present invention. It is to be understood that one or more of the above embodiments may be combined with one or more of the other embodiments, unless explicitly stated otherwise. The invention illustratively disclosed herein suitably may be practiced in the absence of any element or step which is not specifically disclosed or claimed.

Claims

1. A method for making a cross-polarization removing optical film for an optical article, the method comprising:

providing a film having at least a first section comprising a first edge, a second section comprising a second edge, a predetermined color intensity, and a thickness;

providing an apparatus, wherein the apparatus comprises at least a first roller and a second roller, wherein the first roller and the second roller are configured to stretch at least a portion of the film; and

continuously and asymmetrically stretching at least a portion of the film using the apparatus while substantially maintaining the color intensity of the film.

2. The method of claim 1, wherein the method further comprises providing an apparatus wherein the first roller is a substantially cylindrical roller and the second roller is a substantially frustoconical roller.

3. The method of claim 1, further comprising stretching the film such that the thickness of the film is reduced from a first thickness to a second thickness, wherein the second thickness is less than the first thickness.

4. The method of claim 3, further comprising stretching at least a portion of the film such that at least a portion of a first segment of the film has a first stretch ratio and a first polarization efficiency and at least a portion of a second segment of the film has a second stretch ratio and a second polarization efficiency.

5. The method of claim 4, further comprising stretching the film such that the first stretch ratio and the first polarization efficiency are greater than the second stretch ratio and the second polarization efficiency.

6. The method of claim 4, further comprising stretching the film such that a total stretch ratio of the film, including the first stretch ratio and the second stretch ratio, and a total polarization efficiency, including the first polarization efficiency and the second polarization efficiency, continuously decrease from a first edge of the film to a second edge of the film.

7. The method of claim 1, wherein the method further comprises providing an apparatus wherein the first roller is a substantially cylindrical roller or a substantially frustoconical roller and the second roller is a substantially cylindrical roller or a substantially frustoconical roller.

8. The method of claim 4, further comprising stretching at least a portion of the first section of the film such that it has a stretch ratio of between 1 and 4 and a polarization efficiency of between 90% and 100%.

9. The method of claim 8, wherein the method further comprises stretching at least a portion of the second section of the optical film such that it has a stretch ratio of less than 3.5.

10. The method of claim 1, the step of providing the film further comprising providing a pre-stretched film.

11. The method of claim 1, wherein the step of providing the film further comprises providing the film with a color gradient, wherein the color gradient varies continuously from a first edge of a first section of the film to a second edge of the second section.

12. The method of claim 1, wherein the method further comprises further processing the film using at least one of casting, injection molding, additive manufacturing, and tinting.

13. An optical article comprising a cross-polarization removing optical polarizing film, wherein the film comprises at least:

a first segment comprising a first edge, a first stretch ratio, and a first polarization efficiency,

a second segment comprising a second edge, a second stretch ratio, and a second polarization efficiency, wherein the first stretch ratio and first polarization efficiency are greater than the second stretch ratio and second polarization efficiency; and

a polarization gradient that decreases continuously from a first edge of the film to a second edge of the film, an

Wherein the film is continuously and asymmetrically stretched.

14. The optical article of claim 12, wherein the first and second polarization efficiencies comprise a total polarization efficiency, and wherein the total polarization efficiency decreases continuously from a first edge of the film to a second edge of the film.

15. The optical article of claim 12, wherein the film has a transmission of between 8% and 85%.